Environmentally Assisted Cracking: Theory and Practice: Stress Corrosion Cracking II
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Wednesday 2:00 PM
March 17, 2021
Room: RM 18
Location: TMS2021 Virtual
Session Chair: James Burns , University of Virginia; Yiren Chen, Argonne National Lab
2:00 PM Cancelled
Cracking Growth Behavior of Irradiated Stainless Steels in Light Water Reactors: Yiren Chen1; Bogdan Alexanderanu1; Appajosula Rao2; 1Argonne National Laboratory; 2Nuclear Regulatory Commission
Core internal components of light water reactors (LWRs) are exposed to high-temperature coolant and high-flux neutrons during power operations. Such severe service conditions can activate and enhance a wide range of degradation processes in reactor metals, leading to deteriorated corrosion resistance and mechanical performance. To ensure the structural integrity and functionality of core internal components, the mechanisms and the extent of material degradation must be evaluated adequately. In this work, stress corrosion cracking growth rate and fracture toughness tests are conducted on irradiated stainless steel samples in simulated LWR environments. The effects of water chemistry, stress intensity factor, temperature, and material fabrication history on crack growth behavior are evaluated at different irradiation doses. The obtained crack propagation rates and fracture toughness results are compared with the current model predictions for irradiated stainless steels, and are discussed in the context of aging management and long-term sustainability of LWRs.
2:40 PM
Stress Corrosion Cracking of TRIP Fe39Mn20Co20Cr15Si5Al1 (at.%) High Entropy Alloy: Pranshul Varshney1; Rajiv Mishra2; Nilesh Kumar1; 1University of Alabama Tusaloosa; 2University of North Texas
Stress corrosion cracking (SCC) can adversely affect the lifetime of any engineering component. The study of high entropy alloys (HEA) shows excellent mechanical properties but SCC susceptibility is unknown. We have studied SCC behavior of a transformation-induced-plasticity (TRIP) Fe39Mn20Co20Cr15Si5Al1 (at.%) HEA in 3.5 wt.% NaCl solution using slow strain-rate tensile testing (SSRT) on smooth tensile specimens along with the electrochemical behavior of the alloy. The microstructural characterization of the alloy was carried out in as-received condition and after corrosion, test using advanced characterization tools including X-ray photoelectron spectroscopy. The polarization test of the alloy done in 3.5 wt.% NaCl solution revealed corrosion current density as 8.05 x 10-8 A/cm2, markedly lower than the 304 stainless steel (76 x 10-8 A/cm2). The pitting potential of the alloy was 0.089 V. The SSRT result shows a decrease in the elongation and ultimate tensile strength. Further experiments are in-progress to understand mechanistic origin of decrease in ductility of the alloy.
3:00 PM
An Alternate Approach to DCB Specimens for Determining Sulfide Stress Cracking Thresholds: Constant or Increasing Driving Force Specimens: Carl Popelar1; W. Hickey1; James Sobotka1; Julian Hallai2; Yifei Zeng2; 1Southwest Research Institute; 2ExxonMobil Upstream Research Co
Sulfide stress cracking (SSC) is one of the leading causes of premature failure of pipelines and equipment in sour service environments. The threshold stress intensity factor (KISSC) is a critical parameter to the design and development of materials and operating conditions to avoid premature failure. The current standard for determining KISSC involves measuring the arrest toughness of wedge-loaded double cantilever beam specimens exposed to sour environments. However, the known dependence of arrest toughness on the initial loading conditions and challenges in ensuring crack arrest raise uncertainties in KISSC. In this work, we propose an alternative approach for determining KISSC that relies on a novel wedge-loaded fracture specimen with a constant or increasing driving force. This specimen allows KISSC to be more directly determined from crack initiation, thereby eliminating ambiguities in determining KISSC. This paper will review the challenges of the current standard and discuss the benefits of this alternate method.
3:20 PM Invited
The Effect of Loading Rate on Environment-assisted Cracking Behavior in Ti, Fe, Al, and Ni-based Structural Alloys: James Burns1; Zachary Harris1; 1University of Virginia
While literature indicates that the applied loading rate (dK/dt) can affect hydrogen environment-assisted cracking (HEAC) behavior, the quantification of dK/dt dependencies and mechanistic understanding of why the applied dK/dt influences HEAC remain limited. In this study, a slow-rising stress intensity (K) framework was utilized to measure HEAC kinetics over dK/dt ranging from 0.2 to 20 MPa√m/hr in Beta-C Ti, AA7075-T651, AA5456-H116, Monel K-500, and Custom 465-H900 stainless steel immersed in 0.6 M NaCl at applied potentials known to promote modest HEAC susceptibility. Results demonstrate that the crack growth rate (da/dt) exhibits two characteristics regimes of behavior with increasing dK/dt across multiple alloys. In particular, a ‘plateau’ regime where da/dt is independent of dK/dt was observed for elevated dK/dt, while a ‘linear’ regime where da/dt linearly scales with dK/dt was noted for slow dK/dt. The implications of these findings on recent testing standardization efforts for HEAC are then discussed.
4:00 PM
Comparison of Surface Treatment Technologies for the Mitigation of Stress Corrosion Cracking in Al-Mg: Matthew McMahon1; William Golumbfskie1; Eric Dau2; 1Naval Surface Warfare Center, Carderock Division; 2Vision Point Systems
Al-Mg alloys such as AA5083 and AA5456 are of increasing interest for marine construction based on their weldability and high strength-to-weight ratio. However, Mg diffusion to the grain boundaries to form the β phase (Al3Mg2) remains a concern, since this sensitization process enables stress corrosion cracking (SCC) and promotes premature failure in service. One means of combating this phenomenon is compressive surface treatment, which imparts cold work and compressive residual stress into the material to reduce the effective stress experienced at a surface flaw, if it were to form. The present work evaluates two surface treatment technologies, ultrasonic impact treatment (UIT) and laser shock peening (LSP), for their ability to mitigate SCC in marine conditions. These treatments are evaluated by way of the slow rising stress intensity test in simulated seawater to determine the efficacy of each in near worst-case crack growth scenarios.
4:20 PM
Understanding the Effect of Polarization on SCC Resistance and Crack Tip pH of AA6111-T8: Katrina Catledge1; Mark Nichols2; Gerald Frankel1; Jenifer Locke1; 1The Ohio State University; 2Ford Research and Advanced Engineering, Ford Motor Company
6xxx Al-Mg-Si alloys are age-hardenable and considered resistant to stress corrosion cracking (SCC) in comparison to other age-hardened aluminum alloys. Their high strength-to-weight ratio makes them attractive for automotive applications in conjunction with steels and carbon fiber reinforced polymer (CFRP). This research investigates the effects of anodic polarization on the SCC resistance of AA6111-T8 in terms of threshold stress intensity and crack growth rates. Results show that anodic polarization to simulate galvanic coupling with CFRP severely reduces the SCC resistance. Testing under cathodic polarization is underway to verify that H produced during bulk sample cathodic polarization does not cause hydrogen embrittlement. Measured changes in crack tip pH during full immersion fracture mechanics-based cracking experiments will be compared to facilitate understanding of the effect of applied potential on SCC resistance. This work is supported by the Department of Energy under award number DE-EE0007760 through a sub-award under PPG Industries, Inc.